i had a water temp mechanical gage slowly die, put in another one, then had my
oil temp fail, so got an Autometer, which is very similar but not identical to the Smiths, the Bezel is slightly different. Of course, says Autometer. But the first one was likewise bad, but i got it replaced and have been fine ever since. About 49K miles on the rest of them.
I think mechanical gages are probably more accurate, but more tender, too. I consider them a wear out item on a frequently driven car.